Thanks for all the info. My current design uses the QFN part. I don't want to order chips until I know what the demand will be, and I am concerned that they will be out of stock for some months once we are ready to order parts-- this will be for a Kickstarter campaign.
Now that I know more about how Atmel manufacturing works, I think we can work this into the schedule.
Using an Atxmega is also really intriguing, and I'll have to look into this when I get home on Thursday. I brought my brand new laptop with me, a Surface Pro 3, but left the charger at home. Woops. So I'm replying from my phone.